High resolution contact printing

ABSTRACT

Finely detailed photograph images, e.g. microcircuit patterns, made by vacuum contact exposure have improved resolution of detail. A master plate containing a mask image and a sensitized object plate are manipulated from initial positions of separation into extremely close face-to-face contact. Entrapment of air between the plates, which prevents total contact, is avoided by exhausting the space containing the plates while the plates are held discretely separated and only thereafter manipulating the plates into total contact in the exhausted space.

United States Patent Inventors Joseph G. Jordan Poughkeepsie; Robert C. Kammerzell, Hyde Park, both of, N.Y.

Appl. No. 835,321

Filed June 23, 1969 Patented Sept. 14, I971 Assignee International Business Machines Corporation Armonk, N.Y.

HIGH RESOLUTION CONTACT PRINTING l I Claims, 5 Drawing Figs.

Int. Cl G03b 27/20 Field of Search 355/132,

[56] References Cited UNITED STATES PATENTS 3,521,953 6/1970 Tancredi 355/78 Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard L. Moses Anorneysllanifin and .lancin and Robert Lieber ABSTRACT: Finely detailed photograph images, e.g. microcircuit patterns, made by vacuum contact exposure have improved resolution of detail. A master plate containing a mask image and a sensitized object plate are manipulated from initial positions of separation into extremely close faceto-face contact. Entrapment of air between the plates, which prevents total contact, is avoided by exhausting the space containing the plates while the plates are held discretely separated and only thereafter manipulating the plates into total contact in the exhausted space.

PATENTED SEP 1 4 l97l SHEET 1 OF 3 r O um] I I N I ////A r I INVENTORS JOSEPH 6. JORDAN ROBERT C. KAHHERZELL av Wm ATTORNEY PATENTEDSEPMIQII 3604' 800 gum z or a FIG. 3

PATENTEDSEPMIBH 3.604.800

' sum 3 or 3 FIG 5 HIGH RESOLUTION CONTACT PRINTING BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to transfer of photographic images between planar master and object media by the technique of contact printing. In particular the invention concerns a technique and associated apparatus for obtaining the uniform and complete face-to-face contact between master and object plates for a contact print exposure operation.

2. Description of the Prior Art It is generally known that fidelity of reproduction of a photographic image ina contact exposure is affected by the intimacy and uniformity of contact between the image mask medium or master and the image receiving medium or object. Pressure upon touching elements does not produce uniform and total contact over the full contact interface if air is initially present between the elements. The tendency is for the touching elements to flex and form peripheral seals which prevent escape of air from the central space between elements. The trapped air prevents full contact.

Accordingly we have devised the subject technique and apparatus for sequentially: (l) exhausting the intervening airspace between master and object elements of a contact print operation while the elements are held discretely apart; (2) moving the separated elements together into total and uniform face-to-face contact while the intervening space is held exhaus'ted; and (3) subjecting the elements to a contact light exposure while in the condition of uniform contact.

SUMMARY OF THE INVENTION The invention seeks to provide uniformly close face-to-face contact between an image transferring master element and an image receiving object element in a photographic contact printing process. This is especially useful in fabrication of finely detailed devices such as integrated circuits where high resolution image transfer is an important factor in the process of fabrication.

It can be verified that when elements like photographic plates, with flat planar facing surfaces separated by air, are brought together into contact some air is inevitably entrapped centrally. This results in less than complete uniform contact over the total area of potential contact engagement. The reason for this is that as air at the periphery of the intervening space is forced out the element surfaces tend to flex into a peripheral seal preventing evacuation of air from the more central intervening space. In high resolution contact printing such nonuniform contact tends to degrade the resolution quality of the transferred image.

As features of invention which eliminate the foregoing problem we provide a method and associated apparatus for successively: (1) holding master and object elements with facing contact surfaces discretely separated while exhausting the intervening airspace; (2) moving the elements together in the exhausted space into total and uniform face-to-face contact; and (3) retaining the elements in this condition of complete contact while subjecting them to a contact print exposure operation.

Apparatus for performing the foregoing steps of operation comprises, in a preferred embodiment, several members adapted for convenient assembly and disassembly into a number of enclosed compartments and an interior holding fixture or retaining the master and object contact print elements. The compartment forming members have fittings through which exhaust connections can be made to remove air from the enclosure. The members forming the interior holding fixture are provided with means operable to separate and bring together the master and object elements and to hold the elements in either the separated or touching condition while the compartments are in either exhausted or pressurized conditions. The members forming the outermost compartment surrounding the fixture are adapted to admit light or other radiation into the enclosure, to complete the contact print exposure operation, while the master and object elements are being held in uniform contact and while vacuum is being maintained at the contact interface between elements.

These and other objects, features and advantages of the invention will become apparent upon considering the following detailed description of a preferred embodiment which is illustrated in the accompanying drawing. BRIEF DESCRIPTION OF THE DRAWING FIGS. 1-4 of drawing contain sectional views in elevation of a preferred embodiment of apparatus according to the invention for producing contact print exposures, the views showing the various stages of assembly and operation of the apparatus.

FIG. 5 is a sectional view of an alternate embodiment of apparatus according to the invention. DETAILED DESCRIP TION OF PREFERRED EMBODIMENTS FIGS. 14 show apparatus for producing contact prints b the method of the present invention. The several views show the apparatus in various stages of assembly and operation. There are three main members I-3 which when manipulated in a manner which will become apparent as this description proceeds form three separate fully enclosed compartments having separate air exhaust connections through the members. Members I and 2 joined together at hinge 4 form an outer compartment when closed. Members I and 3 together with a connecting bellows member 5 form a first inner compartment of varying size.

Shaft extension 3a of member 3 extends through opening 6 in member I, and through another opening 7 in a bearing plate 8 fastened to the exterior of member 1. Extension 30 terminates in an axle member 3b on which a cammed lever 9 is rotatably supported. Lever 9 with its cammed portion 10 is rotatable about member 3b in clockwise and counterclockwise directions 11 (FIG. 2) for the purpose of displacing member 3 together with bellows 5 relative to section I. O-ring 12 (FIG. 2) seals off the variable inner compartment space 12a formed by members 1, 3 and 5.

Members I3 have a number of exhaust port fittings l4l7 (FIG. 1) which are used to evacuate air from and return air to the various compartment spaces formed by these members. Exhaust fitting 16 in member 1 connects with exhaust fitting 17 in member 3 through flexible tubing member 18 designed to maintain the exhaust connection through the varying inner compartment space 12a.

Member 2 has an exhaust port 20 and a collimating lens 21, made of glass, plastic, or other suitable transparent material. Lens 21 is a window used to admit light for the yet to be described contact exposure operation. O-ring 24 provided for use with members 1 and 2, forms an outer seal for outer compartment space 24a. This O-ring may for convenience be adhered to the edge surface 25 of member 2,. Other O-rings 26 and 27 are respectively provided with or adhered to members 2 and 3 to form seals between respective inner compartment spaces 26a and 27a and the outer compartment space 24a.

As seen in FIGS. 2 and 3 the assembly is closed over a pair of master and object plate elements 28 and 29 to effect contact print exposure of the plates. Master plate 28 contains the negative of the image, e.g., circuit pattern, to be transferred and developed in object plate 29. Plates 28 and 29 are stacked in registration and placed in position over the O-ring 26, so that when members 1 and 2 are in closed position and iever 9 is in the raised or vertical position the plates 28, 29 are touching and objectplate 29 and O-ring 27 form the closure of space 27a, and master plate 28 and O-ring 26 form the closure of space 26a.

In order to achieve total contact between the facing surfaces of plates 28 and 29 the following procedure is utilized:

1. With members I and 2 in closed position over plates 28 and 29 lever 9 is set in vertical position, as shown in FIG. 2.

2. Inner compartment spaces 26a and 27a are exhausted through respective exhaust port fittings 20 and I7. Fitting I7 communicates with a pump or other exhausting mechanism through flexible tubing 18 and exhaust fitting I6 in member I.

3. Inner compartment space 12a (FIG. 2) is exhausted next. At this stage plates 28 and 29 are touching but contact is not uniform and complete due to the presence of air in the still pressurized space between the plates and in the outer compartment space 240. O-rings 26 and 27 are maintaining tight vacuum seals between respective plates 28 and 29 and respective housing members 2 and 3.

4. Lever 9 is thrown clockwise to the depressed horizontal position indicated in FIG. 3 displacing members 3 and 5 away from member 2 and towards member 1. Vacuum maintained in spaces 26a and 27a keeps plates 28 and 29 in sealing connection with respective O-rings 26 and 27 and therefore as member 3 is displaced upwards object plate is also displaced upwards away from master plate 28 leaving the space between plates shown in FIG. 3. Spring clips 24b, 24c are pushed aside by the object plate during this operation.

5. Outer chamber space 24a and the connecting space between the separated plates 28 and 29 is now evacuated through exhaust port fitting 14. Ring clips 24b, 24c mentioned above serve to support the object plate in position during this step.

6. Lever 9 is restored counterclockwise to vertical position (FIG. 4) bringing plates 28, 29 together into touching contact through the now exhausted intervening space. Clips 24b, 240 are again pushed aside by the object plate.

7. Space 12a is pressurized to hold the plates together and then pressure less than that in space 12a is restored to spaces 26a and 27a to force the plates 28, 29 into complete face-toface contact over the total area of potential contact. Contact is total, uniform and unimpeded due to the vacuum between plates. Excellent contact is achieved when space 24a is exhausted to a pressure of 1 millimeter of mercury.

8. With the plates now in the desired state of uniform and complete contact light rays 40 (FIG. 4) emitted from a switchcontrolled source 41, are directed through window 21 and transparent image spaces in master plate 28, impinging on object plate 29 in the desired image transferral pattern. The light is of course pulsed on only for the exposure period required to complete image transferral.

9. Where not already present atmospheric pressure is restored in spaces 12a, 26a, and 27a. Space 24a is then restored to atmospheric pressure and lever 9 is thrown clockwise to retracted (horizontal) position permitting access to the plates for object plate removal and development following separation of members I and 2. Master plate 28 may either be removed with the exposed object plate or, if additional contact prints or reproductions are required, left in place or repetition of the procedure just described.

It may now be seen that the arrangement of apparatus just described represents a unique means for remotely adjusting the relative spacing of a pair of master and object plates so that the space between and surrounding the plates may be evacuated while the plates are held apart and also so that thereafter the plates may be uniformly pressed together into unimpeded total contact. Clearly this arrangement eliminates the problem of irr gular or deformed contact caused by entrapment of air bet een touching plates. Comparative observations indicate that plates fixed in an unadjustable touching position during evacuation, even after extended evacuating periods on the order of 45 minutes, do not reach a state .of contact suitable for achieving contact exposures with a reproduction resolution of 50 microinches, whereas plates manipulated according to the above-outlined procedure reach a state of perfected contact in a matter of seconds.

Those skilled in the art to which this invention pertains will recognize moreover that many elements of the illustrated ap paratus can easily be changed in form and/or position without deviating from the principles of invention just outlined.

For example the lever arrangement (3a, 3b, 9) for controlling the displacement position of member 3 could be replaced 2) fixed a solenoid 9' (pictured in phantom in FIG. 2) fixed to member 1 and attractable to a magnetically permeable plate or the like 3a attached to the upper portion of section 3. Then, the bellows chamber space 12a could be compressed merely by electrically energizing the solenoid, and reexpanded into contact-establishing position simply by deenergizing the solenoid and introducing appropriate pressures successively into spaces 12a, 26a, 27a. In place of the solenoid and plate a double-acting pneumatic cylinder could be used.

Another variant suggested in FIG. 5 would replace the collimating lens window 21 on member 2 with a hinged cover I9 which would be opened at step 8 of the foregoing procedure to accomplish exposure.

We have shown and described above the fundamental novel features of the invention as applied to several preferred embodiments. It will be understood that various omissions, substitutions and changes in form and detail of the invention as described herein may be made by those skilled in the art without departing from the true spirit and scope of the invention. It is the intention therefore to be limited only by the scope of the following claims.

What is claimed is:

1. In a contact printing process of obtaining high resolution radiant energy exposure of an image receiving object through a master image transparency; the steps preceding said exposure of:

holding said master and object spaced apart from each other within an airtight enclosure;

evacuating a portion of said enclosure including the space between said master and object; and

bringing said master and object together into intimate faceto-face contact while maintaining vacuum in said space.

2. In a contact printing process of obtaining high resolution radiant energy exposure of an image receiving object through a master transparency; the steps preceding said exposure of:

holding said master and object spaced apart from each other within an airtight enclosure;

evacuating a portion of said enclosure including the space between said master and object;

bringing said master and object together into intimate faceto-face contact while maintaining vacuum in said space; and

with said master and object in said intimate contact restoring pressure within said portion of said enclosure to the condition preceding the evacuating step.

3. The method of claim 2 with the added step of exposing said object by directing light through a transparent lens section of said enclosure to said master.

4. The method of claim 2 with the added step of:

opening a section of the enclosure providing access to said master for said radiant energy exposure.

5. Apparatus for producing photographic prints by contact printing exposure of an image receiving object element through a master transparency element comprising:

means forming an airtight compartment and contact exposure fixture;

means providing a conduit between the interior space of said compartment and the exterior space surrounding said compartment for selective establishment of vacuum conditions within said interior space;

means adaptive to hold a pair of master and object elements within said interior compartment space separated from each other and facing each other in a parallel relation while vacuum is present in said compartment;

means communicating with said holding means to allow for remote relative manipulation of said facing elements through said evacuated interior space into tight contact engagement with each other;

means providing access to said interior space through said compartment forming means for radiant energy exposure of said tightly contacting elements as required in a contact-printing operation.

6. Apparatus according to claim 5 wherein said access providing means includes a collimating lens forming a window section of said compartment forming means which is adaptive for transferring radiant exposure energy from an exterior source to said tightly contacting elements.

7 Apparatus for rapidly producing on an object plate a photographic contact print of a fine line image contained on a transparent master plate, subject to very close tolerance restrictions on dimensions of the transferred image comprising:

means forming an enclosure surrounding and holding said plates in stacked face-to-face position;

means for introducing a small discrete spacing between facing surfaces of said plates;

means operable in coordination with said spacing means to evacuate the enclosure rapidly while said plates are held with said discrete spacing;

means coordinated with said vacuum producing means for disabling the spacing means and bringing said plates together into intimate face-to-face contact soon after the enclosure becomes evacuated; and

means for exposing said plates to radiant energy effective to cause image transferral from said master plate to said object plate. 8. Apparatus according to claim 7 wherein said exposing means includes a collimating lens window section for transferring said radiant energy from an external source into said enclosure.

9. The apparatus for rapidly yet faithfully transferring a fine line image from a master plate to a sensitized object plate, by a contact exposure to radiant energy and with very close tolerances maintained on fidelity of the transferred image, comprising:

hinged chamber forming means including first, second and third members, said first and second members, joined by a hinge, forming an outer chamber;

said third member being displaceably joined to said first member by a bellows membrane and forming thereby a first inner chamber which is collapsible;

said members each having at least one exhaust opening;

said second and third members together forming a holding fixture for said plates and with respective said plates forming distinct second and third airtight inner chambers which are isolated from each other and from the chamber;

said second member having an opening to admit external radiant energy to expose said plates;

said third member having a displaceable plate holding frame with an exhaust opening, a shaft attached to said displaceable frame and extending slidably through a pressure sealed opening in said first member, and flexible means sealably connecting the exhaust opening in the displaceable frame with a said exhaust opening in the first member;

means for remotely manipulating said shaft and frame of said third member relative to said first member with said first, second and third inner chambers and said outer chamber in predetermined states of evacuation, whereby if a said pair of master and object plates is supported in light contact engagement position between said second member and the holding frame of said third member and vacuum is present in the second and third inner chambers the object plate is held adjacent the third member frame and the master plate is held adjacent the second member; as a consequence of which the plates may be separated leaving a space between said plates connecting with and subject to evacuation with the outer chamber; and whereby with the outer chamber evacuated said plates can be manipulatedferrance of said radiant ex osure eneggy to said plates through said second inner c amber; sal means including a collimating lens.

11. The apparatus of claim 9 with:

means incorporated in said second member to form closure over said opening; said means including a hinged cover plate swingable to closed and opened positions relative to said opening. 

1. In a contact printing process of obtaining high resolution radiant energy exposure of an image receiving object through a master image transparency; the steps preceding said exposure of: holding said master and object spaced apart from each other within an airtight enclosure; evacuating a portion of said enclosure including the space between said master and object; and bringing said master and object together into intimate face-toface contact while maintaining vacuum in said space.
 2. In a contact printing process of obtaining high resolution radiant energy exposure of an image receiving object through a master transparency; the steps preceding said exposure of: holding said master and object spaced apart from each other within an airtight enclosure; evacuating a portion of said enclosure including the space between said master and object; bringing said master and object together into intimate face-to-face contact while maintaining vacuum in said space; and with said master and object in said intimate contact restoring pressure within said portion of said enclosure to the condition preceding the evacuating step.
 3. The method of claim 2 with the added step of exposing said object by directing light Through a transparent lens section of said enclosure to said master.
 4. The method of claim 2 with the added step of: opening a section of the enclosure providing access to said master for said radiant energy exposure.
 5. Apparatus for producing photographic prints by contact printing exposure of an image receiving object element through a master transparency element comprising: means forming an airtight compartment and contact exposure fixture; means providing a conduit between the interior space of said compartment and the exterior space surrounding said compartment for selective establishment of vacuum conditions within said interior space; means adaptive to hold a pair of master and object elements within said interior compartment space separated from each other and facing each other in a parallel relation while vacuum is present in said compartment; means communicating with said holding means to allow for remote relative manipulation of said facing elements through said evacuated interior space into tight contact engagement with each other; means providing access to said interior space through said compartment forming means for radiant energy exposure of said tightly contacting elements as required in a contact-printing operation.
 6. Apparatus according to claim 5 wherein said access providing means includes a collimating lens forming a window section of said compartment forming means which is adaptive for transferring radiant exposure energy from an exterior source to said tightly contacting elements. 7 Apparatus for rapidly producing on an object plate a photographic contact print of a fine line image contained on a transparent master plate, subject to very close tolerance restrictions on dimensions of the transferred image comprising: means forming an enclosure surrounding and holding said plates in stacked face-to-face position; means for introducing a small discrete spacing between facing surfaces of said plates; means operable in coordination with said spacing means to evacuate the enclosure rapidly while said plates are held with said discrete spacing; means coordinated with said vacuum producing means for disabling the spacing means and bringing said plates together into intimate face-to-face contact soon after the enclosure becomes evacuated; and means for exposing said plates to radiant energy effective to cause image transferral from said master plate to said object plate.
 8. Apparatus according to claim 7 wherein said exposing means includes a collimating lens window section for transferring said radiant energy from an external source into said enclosure.
 9. The apparatus for rapidly yet faithfully transferring a fine line image from a master plate to a sensitized object plate, by a contact exposure to radiant energy and with very close tolerances maintained on fidelity of the transferred image, comprising: hinged chamber forming means including first, second and third members, said first and second members, joined by a hinge, forming an outer chamber; said third member being displaceably joined to said first member by a bellows membrane and forming thereby a first inner chamber which is collapsible; said members each having at least one exhaust opening; said second and third members together forming a holding fixture for said plates and with respective said plates forming distinct second and third airtight inner chambers which are isolated from each other and from the chamber; said second member having an opening to admit external radiant energy to expose said plates; said third member having a displaceable plate holding frame with an exhaust opening, a shaft attached to said displaceable frame and extending slidably through a pressure sealed opening in said first member, and flexible means sealably connecting the exhaust opening in the displaceable frame with a said exhaust opening in the first member; means for remotely manipulating said shafT and frame of said third member relative to said first member with said first, second and third inner chambers and said outer chamber in predetermined states of evacuation, whereby if a said pair of master and object plates is supported in light contact engagement position between said second member and the holding frame of said third member and vacuum is present in the second and third inner chambers the object plate is held adjacent the third member frame and the master plate is held adjacent the second member; as a consequence of which the plates may be separated leaving a space between said plates connecting with and subject to evacuation with the outer chamber; and whereby with the outer chamber evacuated said plates can be manipulated without impedance of air into tight face-to-face contact through the evacuated space connecting with the outer chamber for contact print exposure to radiant energy under tightly controlled contact conditions.
 10. The apparatus of claim 9 with: means interposed in said second member opening for transferrance of said radiant exposure energy to said plates through said second inner chamber; said means including a collimating lens.
 11. The apparatus of claim 9 with: means incorporated in said second member to form closure over said opening; said means including a hinged cover plate swingable to closed and opened positions relative to said opening. 